Waveguide device and method of manufacturing this device

ABSTRACT

Waveguide device for guiding a radio frequency signal at a given frequency f, the device including: a core manufactured by additive manufacturing and including side walls with inner and outer surfaces, the inner surfaces delimiting a waveguide channel, wherein a cross-section of the channel has two straight sides joined together by two half-portions, at least one of the two half-portions being rounded or formed of at least two straight segments, the cross-section having a maximum length (a) and a maximum width (b), the ratio between the maximum length (a)/maximum width (b) being between 2.05 and 3.5, preferably between 2.05 and 2.4.

TECHNICAL FIELD

The present invention relates to a waveguide device and a method ofmanufacturing said device.

BACKGROUND

Radio frequency (RF) signals can propagate either in free space or inwaveguide devices. These waveguide devices are used to channel RFsignals or to manipulate them in the spatial or frequency domain.

The present invention relates in particular to passive RF devices thatallow the propagation and manipulation of radio frequency signalswithout the use of active electronics. Passive waveguides can be dividedinto three distinct categories:

-   -   Devices based on guiding waves inside hollow metal channels,        commonly called waveguides.    -   Devices based on guiding waves inside dielectric substrates.    -   Devices based on guiding waves by means of surface waves on        metallic substrates such as PCBs, microstrips, etc.

The present invention relates particularly to the first category above,collectively referred to hereinafter as waveguides. Examples of suchdevices include waveguides per se, filters, antennas, polarizers, modeconverters, etc. They can be used for signal routing, frequencyfiltering, signal separation or recombination, transmission or receptionof signals into or from free space, etc.

Conventional waveguides used for radio frequency signals have internalopenings of rectangular or circular cross-section. They allow thepropagation of electromagnetic modes corresponding to differentelectromagnetic field distributions along their cross-section.

An example of such a conventional waveguide is shown in FIG. 1 frompatent application WO2017208153. It consists of a hollow device, whoseshape and proportions determine the propagation characteristics for agiven wavelength of the electromagnetic signal. The cross-section of theinternal channel of this device is rectangular. Other channelcross-sections are suggested herein, including circular shapes.

The waveguide 1 of FIG. 1 includes a core 3 made by additivemanufacturing by superimposing layers on top of each other. This core 3delimits an internal channel 2 intended for wave guidance, thecross-section of which is determined according to the frequency of theelectromagnetic signal to be transmitted. The core 3 has an innersurface 7 and an outer surface 8, with the inner surface 7 covering thewalls of the rectangular opening 2. The inner surface 7 of the core 3 iscovered with a conductive metal layer 4. The outer surface 8 can also becovered with a conductive metal layer 5, which contributes in particularto the rigidity of the device.

Straight waveguides as in FIG. 1 are often printed with successivelayers perpendicular to the longitudinal z direction, i.e., in avertical position. This allows lateral surfaces of the guide to beprinted in a vertical position and thus avoids the additive printing ofcantilevered portions that are difficult or even impossible to achieve.

However, waveguides are often curved in order, for example, to connectequipment or devices that are not aligned with each other. Waveguideswith bifurcations, e.g., polarizers, or changes in cross-sectional shapeor area, e.g., in order to realize filters or other components, are alsoknown. The additive manufacturing of such curved or non-rectilinearshaped waveguides, however, poses additional difficulties, as portionsof the waveguide core are then necessarily cantilevered during printing.

FIG. 12 illustrates a portion of a rectangular waveguide core 3 duringits additive printing on a horizontal platform 6. The longitudinal zdirection of the waveguide is in this example substantially horizontal,but none of the side surfaces of the waveguide are horizontal. Thisresults in additive layers 30 for printing the core that are notparallel to the sides of the waveguide and furthermore form an angle,for example an angle α1, with the horizontal surface xy of the printingplatform. Most additive printing processes, however, including selectivelaser melting (SLM) processes, require a minimum angle, for example 20or 40°, to avoid the risk of collapsing of a newly depositedcantilevered layer. This makes it impossible to print certain waveguideportions, or at least to print them with the desired precision.

FIG. 13 schematically illustrates the angle α2 that is formed betweenthe additive print layers 30 of a waveguide portion whose longitudinal zaxis is oblique to the x-y plane of the print platform 6.

BRIEF SUMMARY OF THE INVENTION

An aim of the present invention is to provide waveguide devicescomprising a core made by additive printing that are simpler tomanufacture.

An aim of the present invention is to provide waveguide devicescomprising a core made by additive printing that are more robust.

Another aim of the present invention is to provide waveguide devicesthat can be directly connected to various types of equipment or otherwaveguide devices.

According to the invention, these aims are achieved in particular bymeans of a waveguide device for guiding a radio frequency signal at adetermined frequency, comprising:

a core manufactured by additive manufacturing and comprising side wallswith outer and inner surfaces, the inner surfaces delimiting a waveguidechannel,

a cross-section of the channel having two straight sides joined togetherby two half-portions, at least one of the two half-portions beingrounded or formed of at least two straight segments

said cross-section having a maximum length and a maximum width, theratio between the maximum length/maximum width being between 2.05 and3.5, preferably between 2.05 and 2.4.

The two straight sides facilitate 3D printing, especially when thewaveguide is printed with these sections in a vertical, or nearvertical, position, thereby reducing or even avoiding cantileverproblems between a print layer and the overlying layer.

The maximum length preferably extends in a direction parallel to the twostraight sides. The two straight sides preferably form the long sides ofthe section.

The rounded shape or shaped of at least two straight line segments ofthe half-portions functions as a pair of arches connecting the tworectilinear sides to each other, which also facilitates 3D printing byreducing cantilever problems, and on the other hand increases thestability and strength of the device during and after 3D printing.

The rounded shape of the short sides of the waveguide limits the lengthof the cantilever and thus reduces the risk of sagging, or the magnitudeof sagging if it does occur.

This shape also improves the performance of the waveguide by reducingthe attenuation per meter.

In general, the shape of this section has the advantage of facilitatingthe 3D printing of waveguides or waveguide portions, particularly withrectilinear portions that are vertical, close to the vertical, and evenin any orientation with respect to the horizontal.

The term half-portion refers to any curve or open shape that connectsthe end of one of the straight sides to the other end.

The cross section of the channel is preferably oval in shape.

It can be shown that, in a rectangular waveguide according to FIG. 1,the portion of the electric field that is linearly polarized along they-axis parallel to the length has the expression:

${\overset{\rightarrow}{E} = {E_{0y}\mspace{14mu}{\sin\left( {\frac{m\; }{a}x} \right)}e^{j{({{kz} - {\omega\; t}})}}{\overset{\rightarrow}{u}}_{y}}},{m \in {\mathbb{N}}^{*}}$

The portion of the electric field in the waveguide that is linearlypolarized along the x-axis parallel to the width b obeys the sameexpression, replacing a by b and x by y.

The electric field thus undergoes an attenuation in z along thewaveguide. It can be determined that the minimum attenuation is obtainedwhen the ratio between the length a and the width b of the channel isexactly 2. This ratio also favors the filtering of unwanted transmissionmodes. For this reason, waveguides with a rectangular cross-sectiongenerally have a ratio of a/b that is exactly 2.

It has been demonstrated within the scope of the invention thatwaveguides with the described and claimed shape have minimum attenuationwhen the a/b ratio is between 2.05 and 3.5, preferably between 2.05 and2.4, in particular for a value between 2.1 and 2.3, for example 2.2.These values are particularly optimal for waveguides with an ovalcross-section.

Another advantage of this channel geometry is that it reduces the areaof the inner and outer surfaces of the core, and thus the area that mustbe covered with a deposit.

The half portions may be rounded.

The rounded half portions may form half circles.

The term oval is used in this text to refer to any closed shape withoutsharp corners and concave portions, with the possible exception ofridges or septums. The term oval refers in particular to non-circular,preferably non-elliptical, closed shapes with two axes of symmetry (withthe possible exception of ridges or septums).

The cross-section may have two long straight sides connected by twosemicircles.

The inner face of the channel may be provided with a ridge.

The inner face of the channel may have two ridges opposite each other.

The cross-section may progressively evolve from a so-called ovalcross-section in the middle of the device to a rectangular cross-sectionat at least one end of the device. This allows, for example, thecross-section to be adapted to a waveguide or waveguide connector ofanother device, without the need for intermediate adapting parts.

The device may be twisted by progressively rotating said cross-sectionalong at least a portion of the device.

The device may be twisted by progressive rotation of the cross-sectionabout the longitudinal axis of the device along at least a portion ofthe device.

The device may be twisted by progressive rotation of said cross-sectionsimultaneously about the longitudinal axis and at least one other axisof the device along at least a portion of the device.

The device may be curved by progressive rotation of the cross-sectionabout a transverse axis parallel to a straight side of the device alongat least a portion of the device. This enables notably to modify thedirection of signal transmission.

The device can be curved by progressive rotation of the cross-sectionabout a transverse axis perpendicular to a straight side of the devicealong at least a portion of the device. This enables notably to modifythe direction of signal transmission.

The device may include a conductive layer covering the core, saidconductive layer being formed of a metal. This layer allows to make thesurfaces of the waveguide conductive, and to smooth the surfaces of thecore made by 3D printing.

The device may have at least one axis of symmetry and may be made by 3Dprinting of the device by forming multiple layers on a printingplatform, the layers not being parallel to any plane of symmetry.

The invention also relates to a method of manufacturing a waveguidedevice as described or claimed, comprising a step of additivemanufacturing of the core and a step of depositing a conductive layer onthis core wherein the additive manufacturing is obtained by addingsuccessive layers parallel to each other, said layers being non-parallelto said rectilinear sides of the cross-section of the device.

This additive manufacturing by layers oblique to at least onerectilinear portion of the device cross-section provides great freedomfor the additive manufacturing of waveguides having portions oriented inany manner with respect to the plane of the printing platform.

For example, it is possible to print waveguide devices havingcross-sections parallel or perpendicular to the printing plane of thelayers, and at least one other cross-section not parallel to that plane.

The shape of the cross-section as described reduces the magnitude andconsequences of cantilevers in this printing.

Preferably, only the straight sides should be sufficiently verticalduring printing. In an embodiment, the angle between the printing layersand the straight sides is therefore greater than 20°, preferably greaterthan 40°.

BRIEF DESCRIPTION OF THE FIGURES

Examples of embodiments of the invention are shown in the descriptionillustrated by the appended Figures in which:

FIG. 1 illustrates a waveguide portion according to the prior art.

FIG. 2 illustrates a waveguide portion of oval cross-section accordingto an embodiment.

FIG. 3 illustrates a waveguide portion of oval cross-section with alongitudinal ridge according to an embodiment.

FIG. 4 illustrates a waveguide portion of oval cross-section with twolongitudinal ridges according to an embodiment.

FIG. 5 illustrates a waveguide portion of oval cross-section whose endsprogressively evolve to a rectangular cross-section.

FIG. 6 illustrates a waveguide portion of oval cross-section twistedabout an axis according to an embodiment of the invention.

FIG. 7 illustrates a waveguide portion of oval cross-section twistedabout two axes according to an embodiment of the invention.

FIG. 8 illustrates a waveguide portion of twisted and curved ovalcross-section according to an embodiment of the invention.

FIG. 9 schematically illustrates the direction of printing of the coreof a waveguide portion according to different embodiments of theinvention.

FIG. 10 illustrates a waveguide portion whose midsection is twisted.

FIG. 11 is a measurement diagram comparing the linear attenuation of aconventional waveguide of rectangular cross-section and with alength-to-width ratio equal to 2, with that of an oval cross-sectionwaveguide according to the invention and a length-to-width ratio equalto 2.

FIG. 12 schematically illustrates the 3D printing of a waveguide with arectangular cross-section, the printing being performed in a lyingposition with printing planes oblique to some sides of thecross-section, resulting in problematic cantilevered sections.

FIG. 13 schematically illustrates the 3D printing of a waveguide with arectangular cross-section, the printing being performed in a nearvertical position but with printing planes oblique to some sides of thecross-section, resulting in problematic cantilevered sections.

FIG. 14 schematically illustrates the 3D printing of a rectangularcross-section waveguide according to the invention, the printing beingperformed with printing planes oblique to some sides of thecross-section, resulting in problematic cantilevered sections.

FIG. 15 illustrates a waveguide cross-section comprising two rectilinearsides connected to each other by two half-portions each formed of atleast two straight line segments according to an embodiment.

FIG. 16 illustrates a waveguide cross-section having two rectilinearsides connected together by one arcuate half-portion and anotherhalf-portion formed of at least two straight segments, according to anembodiment.

FIG. 17 illustrates a waveguide cross-section having two straight sidesconnected together by a half-portion formed of at least two straightsegments and another straight half-portion according to an embodiment.

EXAMPLES OF EMBODIMENTS OF THE INVENTION

The waveguide 1 of the various described or claimed embodiments, forexample that of FIG. 2, comprises a core 3, for example a core made ofmetal (aluminum, titanium or steel), or of polymer, epoxy, ceramic, ororganic material.

The core 3 is manufactured by additive manufacturing, preferably bystereolithography, selective laser melting or selective laser sintering(SLS) in order to reduce surface roughness. The core material can benon-conductive or conductive. The wall thickness of the core is forexample between 0.5 and 3 mm, preferably between 0.8 and 1.5 mm.

The shape of the core may be determined by a computer file stored in acomputer data medium.

The core can also be made up of several parts formed by 3D printing andassembled together before plating, for example by gluing or thermalfusion or mechanical assembly.

This core 3 defines an internal channel 2 for guiding waves. The core 3therefore has an inner surface 7 and an outer surface 8, the innersurface 7 covering the walls of the oval cross-section opening 2.

The inner surface 7 of the core 3 is preferably covered with aconductive metal layer 4, e.g. copper, silver, gold, nickel etc., platedby electroless plating. The thickness of this layer is for examplebetween 1 and 20 micrometers, for example between 4 and 10 micrometers.The coating may also be an assembly of layers and comprise, for example,a smoothing layer directly on the core, one or more bonding layers, etc.

The thickness of the conductive coating 4 must be sufficient for thesurface to be electrically conductive at the chosen radio frequency.This is typically achieved with a conductive layer whose thickness isgreater than the skin depth 6.

The outer surface 8 of the channel is preferably also covered with ametallic layer that notably enables to stiffen the device, and to giveit the required strength.

The waveguide channel may include a septum not shown to act as apolarizer to separate the two orthogonal polarities of a signal. Theheight of the septum may be variable, for example with stair steps.

In any embodiment, the waveguide channel may additionally be ridged, asdiscussed below.

At least one end of the waveguide may include a flange or flanges notshown to connect it to another waveguide device or equipment.

The waveguide is, for example, intended for use in a satellite toconnect communications equipment, such as a radio frequency transmitteror receiver, to an antenna or antenna array. One end of the waveguidemay be shaped as an antenna.

The shape and proportions of the cross-section of this channel isdetermined according to the frequency of the electromagnetic signal tobe transmitted and according to the attenuations of differenttransmission modes.

In the embodiment shown in FIG. 2, the cross-section of the channel 2through the waveguide is oval and has two parallel straight portions andtwo rounded short sides. The maximum length a of the channel in the xdirection is equal to a and the maximum width of the channel in the ydirection, i.e., between the straight sides, is equal to b.

The ratio of the maximum length a of the channel to its maximum width bin a conventional waveguide with a rectangular cross-section istypically 2. This value has been determined empirically to be the valuethat produces the lowest attenuation per linear meter.

According to the invention, it has been determined by tests andsimulations that in the case of a waveguide channel having the ovalshape as described, the ratio between the maximum length a of thechannel and its maximum width b is greater than 2, preferably between2.05 and 2.4, for example between 2.1 and 2.3, preferably 2.2.

FIG. 11 shows the signal attenuation per linear meter as a function offrequency for a rectangular waveguide channel with an a/b ratio of 2(upper curve) and with a waveguide channel as described and an a/b ratioof 2.2. As can be seen from these measurement results, the losses causedby transmission in an oval waveguide channel as described are thereforelower than the signal losses in a conventional waveguide channel,provided that the ratio of maximum length a to maximum width b ischanged to, for example, 2.2.

As an example, in an embodiment, the waveguide device is suitable fortransmitting signals in a frequency range between 26.5 and 40 GHz. Thedimension b may be 3.556 mm, and the dimension a may be 7.823 mm. Theradius of curvature r of the curved ends is therefore b/2=1.778 mm.

In the embodiment shown in FIG. 15, the waveguide cross-section has twostraight sides joined together by two half-portions formed by N linesegments, where N is greater than or equal to 2. In this example, eachhalf-portion is formed by 2 straight segments. Half portions formed by3, 4 5 or 6 straight segments, for example, can also be made. The lengthof the segments is preferably equal and the angles between segmentsequal, in order to best approximate the semicircle shape.

In the embodiment shown in FIG. 16, the waveguide cross-sectioncomprises two straight sides connected to each other by an arcuatehalf-portion and another half-portion formed, as in the example above,of N straight line segments.

In the embodiment shown in FIG. 17, the waveguide cross-sectioncomprises two straight sides connected to each other by a straight halfportion and another half portion formed, as in the example above, of Nstraight segments.

As illustrated in FIG. 3, the inner surface 7 of the channel may beprovided with a ridge 20 on one of the long sides, in order to controlthe transmission modes. The height of this ridge may be variable. Theridge 20 may be straight, as shown, or twisted. The inner surface mayalso have a septum not shown.

As shown in FIG. 4, the inner surface 7 of the channel may be providedwith multiple ridges 20, such as two ridges facing each other onopposite long sides, to control transmission modes. Waveguides withthree ridges at 120° from each other, or four ridges at 90° from eachother, can also be made.

As illustrated in FIG. 5, the cross-sectional shape of the channel 2 canchange gradually from, for example, an oval shape as described above inthe middle of the waveguide, to a rectangular shape at one or both ends11,12 of the waveguide 1. The transition can be made over a smallportion of the length of the device, for example, a portion less than 10mm, for example, a 5 mm portion. This change in shape allows for adevice with an oval cross-section along most of its length, with theadvantages described above, but which can be connected directly towaveguides or equipment with a rectangular cross-sectional waveguidechannel. The transition may also include a change in the ratio of themaximum length a to the maximum width b of the channel 2, so as tochange, for example, from a ratio of between 2.05 and 2.4 for theintermediate oval portion to a ratio of 2 at the end(s).

In an embodiment not shown, the cross-section of the channel 2 retainsits shape or type of shape along its entire length, however, theproportions between the length a and width b of the channel aregradually changed.

As illustrated in FIG. 6, the waveguide 1 may be twisted. For thispurpose, the cross-section of the channel 2 undergoes a progressiverotation along the longitudinal direction of the guide, for example, arotation about the longitudinal axis z. In FIG. 6, the rotation betweenthe two ends of the waveguide is 90° so that the longest length a of thechannel 2 that is in a horizontal plane at one end of the waveguide isin a vertical plane at the other end.

Progressive rotation of the waveguide cross-section about the x-axisand/or the y-axis may also be achieved.

As illustrated in FIG. 7, the waveguide 1 may also be twisted byprogressive rotation of the cross-section simultaneously about thelongitudinal (z) axis and at least one other axis of the device, in thiscase the y axis.

As illustrated in FIG. 8, the waveguide 1 can also be curved and thuschange its longitudinal direction, through progressive rotation of saidcross section about the transverse axis (x) of the device. This rotationcan occur over a limited portion of the length of the waveguide, whichthus comprises as in the example successively a straight portion, acurved portion and a second straight portion. The waveguide device maybe curved about the longitudinal z axis of the channel.

FIG. 10 illustrates a waveguide device with an oval cross-section,having two straight end portions and a central portion 10 twistedthrough 90° so that one end of the device is rotated, for examplethrough 90°, relative to the opposite end.

As mentioned, the core 3 of the device is made by 3D printing, forexample by stereolithography or by deposition or hardening of successivelayers. As illustrated schematically in FIG. 14 showing a waveguidebeing printed, printing waveguide devices with complex shapes, forexample curved, twisted devices, having bifurcations or changes in thecross-section of the guide channel, may imply that on at least somecross-sections the printing layers are not parallel to the printingplate, i.e., horizontal. The vaulted shape of the short sides of thechannel 2, however, makes it possible to limit the length of thecantilevered portions, and thus to reduce the risk and/or the amplitudeof the collapse of these portions before being hardened. This vaultedshape is also inherently stronger and more rigid than a lintel shape asin a rectangular cross-section waveguide, so that the channel geometryis better preserved before and after hardening of the printing layers.It can also be seen in this figure that the rectilinear shape of thelong sides makes it easier to print the layers that make up the longsides, especially if the printing is done with the long sidesrectilinear and extending vertically or substantially vertically.

The rectilinear surfaces of the waveguide device are preferably orientedvertically, or at least at an angle greater than 20°, preferably greaterthan 40°, to avoid the risk of deformation of these surfaces.

The term “oval-shaped” in this description and in the claims does notexclude substantially oval shapes as defined above, but including one ormore ridges or septums, or one or more holes. Nor does the term“straight” exclude the presence of a ridge, septum or hole.

REFERENCE NUMBERS USED ON FIGURES

-   1 Waveguide device-   2 Channel (waveguide opening)-   20 Ridge-   3 3D printed core-   4 Internal metal coating-   5 External metal coating-   6 Printing platform-   7 Inner surface-   8 Outer surface-   10 Intermediate portion of a waveguide device-   11 End portion 1-   12 End portion 2-   a Longest length of the channel-   b Width of the channel, in a direction perpendicular to a-   x,y x,y Orthogonal axes in the plane of the channel cross section-   z Longitudinal axis of the channel-   z1 Axis perpendicular to the deposition layers during 3D printing of    the core-   α Angle between a surface of the device and the printing platform.

What is claimed is:
 1. Waveguide device for guiding a radio frequencysignal at a given frequency f, the device comprising: a coremanufactured by additive manufacturing and comprising side walls withinner and outer surfaces, the inner surfaces delimiting a waveguidechannel, wherein a cross-section of the channel has two straight sidesjoined together by two half-portions, at least one of the twohalf-portions being rounded or formed of at least two straight segmentssaid cross-section having a maximum length and a maximum width, theratio between the maximum length and the maximum width being between2.05 and 3.5.
 2. The device of claim 1, said cross-section of thechannel being oval cross-section.
 3. The device of claim 1, the two halfportions being rounded.
 4. The device of claim 3, said rounded halfportions forming semicircles.
 5. The device of claim 1, wherein theinner surface of the channel is provided with at least one ridge.
 6. Thedevice of claim 1, the inner surface of the channel being provided withtwo ridges on said long straight sides, the two ridges facing eachother.
 7. The device of claim 2, said cross-section of the channelprogressively evolving from the middle of the device from said ovalcross-section to a rectangular cross-section at one end of the device.8. The device of claim 1, being twisted by progressive rotation of saidcross-section along at least a portion of the device.
 9. The device ofclaim 8, being twisted by progressive rotation of said cross-sectionabout the longitudinal axis of the device.
 10. The device of claim 6,being twisted by progressive rotation of said cross-sectionsimultaneously about the longitudinal axis and at least one other axisof the device.
 11. The device of claim 1, being curved by rotation ofsaid cross-section progressively along at least a portion of the deviceabout the transverse axis of the device parallel to a said straightside.
 12. The device of claim 1, being curved by rotation of saidcross-section progressively along at least a portion of the device aboutthe transverse axis of the device perpendicular to a said straight side.13. The device of claim 1, comprising a conductive layer covering saidcore, said conductive layer being formed of a metal.
 14. A method ofmanufacturing a waveguide device of claim 1, comprising a step ofadditive manufacturing of said core, wherein said additive manufacturingis obtained by adding successive layers parallel to each other, saidlayers being non-parallel to said straight sides.
 15. The method ofclaim 14, said layers being oblique to said straight sides.
 16. Themethod of claim 15, wherein the angle between said layers and saidstraight sides is greater than 20°.
 17. The method of claim 15, whereinthe angle between said layers and said straight sides is greater than40°.
 18. The device of claim 1, wherein the ratio between the maximumlength and the maximum width being between 2.05 and 2.4.